By Ryan Lee Price
The 305 cubic-inch engine in the Koenigsegg One “megacar” is capable of producing 1,360 horsepower from its gas-powered V8, propelling the 1,360-kg car to a top speed of 280 mph in 20 seconds. That’s a lot of power, and one can’t help but to imagine 1,360 horses hitched to the front of the $1.5 million car attempting to pull it up to 280 mph. However, in either guise—engine or horse team—1,360 horsepower represents the work of a lot of horses, and to understand how the term has been applied to cars, we have to go back about 100 years before cars were even invented.
Let’s start with James Watt, a Scottish boy with an innate intelligence that complemented the homeschooling his mother provided until her death in 1754 (when James was 18). Watt studied instrument making for a year in London before returning to Scotland to set up his own shop in Glasgow. Because he hadn’t been an apprentice for the required seven years, the Glasgow Guild of Hammermen blocked his efforts. It wasn’t until two professors at the University of Glasgow, Joseph Black and Adam Smith, had very specialized instruments that needed repair, and the fact that there were no other instrument makers in all of Scotland, that Watt was able to start his workshop on campus.
In 1759, John Robison introduced Watt to the concept of steam used as a source of power. In the middle of the 18th Century, 
the most widely used steam engine was the Newcomen engine, an atmospheric engine invented in 1712 by Thomas Newcomen, used to pump water out of wells (it was the primary reason to have a steam engine at the time).
Watt was intrigued, not only as a scientist, but as a businessman looking for a new venture. Having never even seen a steam engine at work, Watt tried to build several versions of improved engines and conducted a variety of experiments, coming to the conclusion that the Newcomen engine—which hadn’t been improved upon in 50 years—was wildly inefficient, losing 75 percent of its potential energy to heating the engine cylinder on every cycle.
With financial help from friends, Watt developed a way to condense the steam in a separate chamber, allowing the cylinder’s temperature to remain constant, so heat from the steam could be used for work. By 1776 the first engines were installed, mostly used for pumping water from mines.
The concept of horsepower had been used for nearly 75 years by then. Thomas Savery, who held the patent for an early steam engine (from where we get the term “fire engine”), wrote in his book “The Miner’s Friend; or, An Engine to Raise Water by Fire,” a description of the work his engine could do compared to a horse. James Watt took the concept a little farther in an effort to market his engine to farmers and miners who had only used horses for such work. Watt defined one horsepower as the amount of work required from a horse to pull 150 pounds out of a hole that was 220 feet deep. Watts calculated the kinetic energy as 33,000 foot-pounds per minute (equal to 745 watts or 550-foot-pounds per second of power). To put it into like terms, one horse can raise 330 pounds 100 feet in a minute. This is the power of one horse.
From this, Watt coined the term horsepower and although an overstatement, it has endured over the centuries as a lasting marketing tool to sell farm implements designed to replace horses. Using it to describe the power output of cars is apt, because in the early days of the auto industry “horseless carriages” were replacing the horse, literally.
Though inconvenient, the term is mathematically comparable and still very widely in use, as long as you’re in the United States that is. Most other countries (Europe specifically) have switched to expressing power in watts, which brings us back to the Koenigsegg One “megacar,” so called because it is the first megawatt car (with an equal power-to-weight ratio, one watt per pound).
But how much is one horsepower and what can you do with it? Not much beyond powering a lawnmower. Typical cars these days weigh about 4,100 pounds, and with conventional one-to-one gearing, a single horsepower will make a lot of noise and do nothing. However, with proper gearing, a single horsepower could pull a house off its foundation; albeit very slowly. A car of average size won’t see any considerable movement until the engine reaches about 20 horsepower, which can propel it approximately 50 miles an hour (but you’re not going to win any drag races with it). The first Volkswagen Beetle employed 24 horsepower engines, while the current ones are around 200 hp.
When your patrons are looking to compare their engine’s horsepower, they can turn to Gale’s ChiltonLibrary. Chilton also has many other specifications , such as how much engine oil is needed for an oil change and how much coolant is needed for the radiator. This comprehensive, easy-to-use online resource for novice do-it-yourselfers to serious car buffs covers repairs, maintenance and service information on the most popular cars, trucks, vans and SUVs on the road today. Users will find step-by-step service procedures with video and animation, maintenance and specifications tables, Recalls and Technical Service Bulletins, and vacuum and wiring diagrams…everything needed to do the job right.
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About the Author
Not only is Ryan Lee Price a freelance writer specializing in automotive journalism and a former long-time magazine editor, he is part of the technical editorial team that provides content for most all of the ChiltonPRO and ChiltonDIY products. He currently resides in Corona, California, with his wife Kara and their two children.
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